US2398739A - Catalytic cracking process - Google Patents

Description

April 16,1946. 13.5.` GREENSFELDER ETAL 2,398,739

CATALYTIC CRACKING' PROCESS Filed April 6, 1945 52pm-afar Reqznczmfor Ragznarfor Reader inventors: Esas-nerd rangsfaldar 'ianlms ZmPerrg Patented Apr. 16,1946- l UNITED CATVALYTIC CRACKING PROCESS Bernard S. Greensfelder, Oakland, and Stanley Z. Perry, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application April 6, 1945, Serial No. 586,925

(Cl. ISG-52) Claims.

This invention relates to an improved method for the production of valuable gaseous and normally'liquid hydrocarbon products from various hydrocarbon oils by means of catalytic cracking.

An object of th'e invention is to provide a process for the 'catalytic cracking of various hydrocarbon` oils which aords particularly excellent yields of valuableolefins. Another object cf the invention is to provide such a process wherein hydrocarbon oils may be converted into valuable liquid and gaseous products with a minimum formation of coke, carbon and similar undesired products. Still another object of the invention is to provide a process for the catalytic cracking of hydrocarbon oils which may be carried out in small reactors with large production capacity.

In copending application, Serial Number 545,- 402, filed July- 17, 1944, of which the present application is a continuation-impart, there is described an improved cracking process in which the catalytic cracking is carried out at a temperature above 1000 F. and preferably betwen 1200 F. and 1400F. with a powdered solid adsorptive cracking catalyst diluted with such anamount of a substantially non-catalytic, non-adsorptive and non-combustible mineral diluent that the depth of cracking is maintained below yabout '70% and/or that no cooling is required in the regeneration of the catalyst. The present application is a continuation-impart of saidcopending application. y

The process of the invention is restricted to the catalytic conversion of hydrocarbon oils with solid catalysts in which the catalyst is recycled in the formv of a powder through a zone wherein the conversion is effected under certain specined g iluid catalyst" system wherein the catalyst is employedinfthe so-called "iluidized or pseudoin most allof these various systems. It maybe very advantageously carried out in a "fluid catalyst system, and most advantageously carried out in the somewhat modiiled fluid catalyst system hereinafter described. Since the invention' is particularly advantageous for catalytic cracking in fluid catalyst systems, the particulars of the invention will be described in connection with such systems. It will be understood, however, that the invention is not limited to this particular application. l t

In catalytic cracking in the above-mentioned types of systems there are at present two more or less distinct types of operation known as low temperature cracking" and high temperature cracking, respectively. Low ltemperature catalytic cracking refers to the more usual operation carried out `at temperatures below about 900 F., usually between about 700 F. and 850 F. High temperature catalytic cracking refers to the op eration at temperatures above about 900 F., usually about 925 F. High temperature catalytic cracking has been carried out at temperatures approaching 1000 F. in at least two instances and this is considered to be the upper temperature limit of such operations. It is possible to operate at even higher temperatures, but such operation when carried out in the conventional manners give vastly inferior results as determined by yields, product quality, amount of carbon or coke formed, 'catalyst life, and cost of operation. No

` practical or advantageous method of utilizing such temperatures is available and consequently such operation is'beyond the realm of application.

According to the process of the invention hydrocarbon oils are catalytically cracked atV temperatures above 550 C. or 1022 F., and preferably between 1200 F. and 1400 F., under'such conditions and in such a manner that improved,

f geous subclass of such systems is theso-called'i liquid state. A typical fluid catalyst system is described in Ind. Eng, Chem. 35, 768-773 (1943) The process ofthe invention may be carried out rather than inferior-results are obtained. According to the process of the invention not only is the catalytic cracking carried out at temperatures beyond those considered useful in the conventional so-called high temperature catalytic cracking process, but the regeneration of the catalyst is also carried .out at temperatures above those generally considered applicable. The regeneration temperature in the process of the invention is at least 50 C. (90 F.) above the reaction temperature and therefore above 600 C.

(l112 FJ. Preferred temperatures are between about 1200 F. and 1500 F Many voi the most commonly used catalysts are not capable of withi standing regeneration by the conventional methods at temperatures much above 1100 F. without 5 l catalyst.

In the catalytic cracking of hydrocarbon oils the catalyst becomes deactivated relatively rapidly due to the deposition of carbonaceous cokelike deposits. In order to operate continuously the catalyst is continuously recycled through a separate regeneration zone wherein these carbonaceous deposits are removed by burning, The burning of the carbonaceous deposits liberates a large amount of heat and the amount of heat liberated is more or less proportional to the amount of coke or carbonaceous material deposited in the cracking step, In a typical commercial fluid catalyst cracking plant, for instance, about 13,000`-l6,000 pounds of coke are burned perl hour. It is at present considered necessary to retain the temperature of the catalyst in the regeneration at about 1100 F. or below. A portion of the heat of combustion is taken up in heating the regeneration gases and in raising the temperature of the catalyst. By far the major amount of the heat of combustion is removed by the use of suitable coils, or more generally by recycling a portion of the catalyst undergoing regeneration through an external cooling device.` This cooling (extraction of heat) during the regeneration is difficult to effect evenly and eiciently and is. furthermore, wasteful. In the process of the invention the amount of cooling required in the regeneration is very much less and in a preferred embodiment of the invention no cooling at all is necessary.

If it is attempted to operate the catalytic cracking process at these high temperatures with the conventional catalysts in the otherwise conventional manners it is found that the results'obtained (except the depth 'of cracking) are much inferior to those obtained using the conventional high temperature cracking process in which the cracking is carried out at temperatures from 'about 900 F. up to about 1000 F. Although the depth of cracking is materially increased the yield of valuable hydrocarbon gases such as the butylenes and propylene'are low and the gasoline produced is of poor quality. Also it is found that the losses to coke and carbon, and consequently the amount of cooling required to maintain the regeneration temperature, are much increased.

Thus, it is found that as the conversion per pass is increased, particularly in the region of (i5-'70% conversion, the rate of carbon or coke deposition increases rapidly, (Depth of cracking is dened as 100- minus the percent by weight of the original feed recovered as an oil boiling above This is illustrated in the following table: Y v

Tinta Carbon formed in cracking second cut straight 4 Per cent Depth of cracking cubo Thus by increasing the depth of cracking from to r70% (8% increase) the rate of carbon formation is increased 26%.

Contrary to expectation, however, it is found that for a given depth of cracking the rate of carbon formation decreases as the temperature of the catalytic cracking is increased. Thus, by limiting the depth of cracking according to the process of the invention the yield of coke or other carbonaceous deposits (calculated as carbon) may be considerably decreased.

Also it is found, contrary to expectation, that unlike the yields of hydrogen, methane, ethane. propane, butanes, pentane and ethylene, the yields of propylene, butylenes and amylenes pass through pronounced maxima as the depth of cracking is increased, and that these maximum yields in each case correspond to' a depth of cracking between about 60% and '70% when operating at temperatures above 1000 F. When operating at '750 F., on the other hand, these maxima are barely noticeable and furthermore correspond to a depth of cracking of about 45%. Thus, by controlling and limiting the depth of cracking maximum yields of these valuable products may be obtained. Although the yields of ethylene do not go through such a maximum, the yields of ethylene are also much greater than those obtained by conventional high temperature operation. Also, although the yields of undesired gases such as methane and ethane are higher than those obtained in the conventional cracking processes, they are lower than could be obtained without limiting the depth of cracking to the specied limits.

The depth of cracking is controlled and retained below about and preferably between 60% and 70%, by employing very high space velocities and by employing a mixed catalyst consisting of the adsorptive cracking catalyst having a high activity and a substantially non-catalytic, non-adsorptive and non-combustible mineral diluent, These two controls are interdependent. The space velocity, measured in terms of the tons of hydrocarbon oil feed charged per hour per ton of the catalyst 1n the reactor, and designated weight hourly space velocity is preferably above 6 and usually between about 6 and 10. Based on 4the more active component of the catalyst mixsacarse eral ldiluent which has substantially no inner surface and is therefore substantially non-adsorptive. When such a catalyst mixture is used substantially all of the cokeis formed on and by the active catalyst component and very little if anyv is formed on or by the inert component.`

Thus, although the rate of coke formation with respect to the active catalyst' remains the same,v

the concentration of coke in the mixed catalyst is reduced. By adjusting the relative proportions of theA two catalyst components the depth vof cracking can be controlled and maintained within the desired limits. Also by suitable adjustment of the space velocity the relative proportions of the two catalyst components may be such that the regeneration may be carried out with undiluted air with little or no cooling. Suitable non-combustible, non-adsorptive inert materials which can be used in the process of the invention are, for example, alpha alumina, sand, powdered quartz, powdered silicon, siliceous tailings from ore dressing processes, powdered pumice, ground slag (provided that it does not catalyzecarbon formation) ground magnesite,-ground dolomite, and the like. Also certain materials like bentonite and diatomaceous earth can be used since under the high temperature conditions prevailing they quickly lose any activity that they might initially have. These various materials are pref'- erably used in the form of particles of about the same size range as the catalyst. For instance, in

are commonly used in catalytic cracking. It is forced by pump 2 through coil 3 of a suitable heater l. The preheated oilleaving the preheater via line 5 picks up a regulated amount of hot freshly regenerated catalyst entering via standpipe t. The catalyst consists, for example. oi a substantially completely regenerated mixture of 60% synthetic silica-alumina-zirconia cracking catalyst having a surface area of about 150 square meters per gramand 40% of powdered silica. The powdered catalyst, at a temperature of about 1250 F., is dispersed with-air entering via line l so that the resulting mixture is about by volume of catalyst. The amount of catalyst introduced is, for example, about 15 parts by weight per part of oil, The preheated oil, upon contacting the catalyst is immediately heated ,to about 1150 F. Part of the heat comes from the catalyst and part of it cornes from the combustion of about 0.5% ci the oil feed. The mixture of oil and catalyst passes via line 5 into bottom draw-oi reactor 8 wherein the oil vapors areV contacted with uidized catalyst at an effective tion of naphtha and gaseous products may be fluid catalyst crackingthe inert material may suitably be a powder passing a 100 mesh sieve.

It will be appreciated that the catalytic cracking according to the present invention is carried out attemperatures much above those necessary for thermal cracking. Most oils to`be cracked begin to undergo thermal cracking at temperatures in the neighborhood of 700825 11A/If any appreciable amount of thermal cracking is, however, allowed to take place the yieldand quality oi the products are considerably reduced. In order to prevent any substantial thermal cracking from taking place the oil to be cracked is preheated toincipient cracking temperatures only and then the preheated oil is rapidly heated to the desired cracking temperature in the presence of the cracking catalyst. This is eil'ected. either entirely by the catalyst or by the catalyst and a partial combustion in the presence ,of the catalyst. Thus the desired cracking temperatures may be reached almost instantaneously upon introducing the hot regenerated catalyst into theoil. In a preferred modification oi the process of the invention, however,` the hot regenerated catalyst is mixed with air and this mixture is in-` troduced into the preheated oil, In a; typical case the hot regenerated catalyst withdrawn from the regenerator is mixed with air to form a `miirture having about 80% by volume of air and this mixture is introduced into the preheated oil; the

taken oi overhead to a condenser IIAand separator I2. Gaseous products may be removed from the separator via line I3 and treated in any conventional manner. A part of the liquid conden sate may be recycled via line Il to serve as reflux and the remainder may be withdrawnvia line I5. Light gas oil may be removedvia line I6, and

heavy gas oil may be removed via line I'I, A

heavy oil may be removed via line I8. These various higher boiling products may be recycled to the catalytic cracking step or treated orutilized in any of the conventional manners,

Partially spent catalyst is continuously withdrawn from reactor 8 via standpipe I9. This partially spent catalyst is picked up by a stream of partially spent regeneration gas and carried via line 20 to a low temperature regenerator 2l. The temperature in regenerator il is for example. between about 1000 F. and 1100 F.: the residence time of the catalyst therein is suillcient to remove only a portion of the carbonaceous deposits. The partially regeneratel catalyst is continuously withdrawn via standpipe 22. This catalyst is picked up byga stream of undiluted air forced in by blower 23 and is carried via line 24 to a high temperature regenerator 26. The regenerationin regenerator 25 is carried out at a temperature of about 1250 F. and the residence time of the catalyst therein is sufficient to insure 4is continuously withdrawn via standpipe 8 as deair burns between about 0.25% and 1%' of the l I oil feed and the liberated heat is utilized in raising the temperature of the oil vapors,

Certain' aspects of the invention may best described in connection with an operation comi prised within its scope.V To aid in'this description reference is had to the attached drawing wherein there is shown by meansof diagrammatic figures not drawn to scale some of the apparatus cracked enters via line I. 'I'he feed may be a naphtha, gas oil. reduced crude, or in fact any of the oils boiling above 155 C. (311 P.) such as and flows of a modified iluid catalyst cracking plant. Referring to the drawing, the oil to be scribed.` YThe partially spent regeneration gas or a portion thereof may be cycled via line 20 to the low temperature regenerator 2|. Additional air may be supplied to the lowtemperature regenerator via line 26. As pointed out. part of the air is passed via ,line 1 to regenerated catalyst in lstandpipe 8. In this vtwo-temperature method of catalyst regeneration much higher temperatures may be employed in the second, or high temperavture step without damaging the catalyst.

We claim as our invention:

1. Aprocess for the catalytic cracking of hydrocarbon oils boiling above about 311911'. which comprises preheating the oil to be cracked to anincipient cracking temperature between about '700 F'. and 825 F., combining the preheated oil with a mixture of air and a hot regenerated catalyst consisting of a iinely divided adsorptive silicaalumina-zirconiacomposite cracking catalyst diluted with such an amount of a finely divided substantially non-adsorptive and non-combustible mineral diluent as to aord a depth of cracking between 60 and 7 0%, said catalyst being at a temperature at least 90 F. above the cracking temperature and the amount of said air-catalyst mixcracking temperature in the range of 1200 F.- 1400 F., retaining said oil in contact with said catalyst at said cracking temperature for a period of time corresponding to a. weight hourly space velocity between about 6 and l0, separating cracked products rich in normally gaseous olens from the catalyst, partially regenerating the cata-V lyst and then completing the regeneration of the catalyst in a separate step by burning with air at a temperature between l200 F. and 1400 F. without cooling. v

2. A process for the catalytic cracking of hydrocarbon cils boiling above about 311 F. which comprises preheating the oil to be cracked to an incipient cracking temperature between about '700 F. and 825 combining the preheated oil with a mixture of air and a hot regenerated catalyst consisting of s, nely divided adsorptive cracking catalyst diluted with such an amount of a finely divided substantially non-adsorptive and non-combustible mineral diluent as to aiord a depth of cracking between 60 and 70%, said catalyst being at a temperature at least 90 F. above the cracking temperature and the amount of said air-catalyst mixture being adjusted to heat the preheated oil to a cracking temperature in the range of l200 F.l400 F., retaining said oil in contact with said catalyst at said cracking temperature for a period of time corresponding to a weight hourly space velocity between about 6 and 10,'separating cracked products rich in normally gaseous olelns from the catalyst, partially regenerating the catalyst and then completing the regeneration of the catalyst in a. separate step by burning with air at a temperature between l200 F. and 1400 F. without cooling.

3. A process for the catalytic cracking of hydrocarbon oils Aboiling above about 311 Fgwhich comprises preheating the oil to be cracked to an incipient cracking temperature between about '700 F. and 825 F., combining the preheated oil with a mixture of air and a hot regenerated catalyst consisting of a nely divided adsorptive silicaalumina-zirconia composite'cracking catalyst dilluted with such an amount oi a finely divided substantially non-adsorptive and non-combustible mineral diluent as to afford a depth of cracking ture being adjusted to heat the preheated oil to a secarse -between and '70%. said catalyst being at a. temperature at least F. above the cracking temperature and the amount of said air-catalyst mixture being adjusted to heat the preheated oil to a cracking temperature above about 1022 F., retainingsaid oil in contact with said catalyst at said cracking temperature for a period of time corresponding to a weight hourly space velocity of at least 6, separating cracked products rich in normally gaseous olefins from the catalyst, and regenerating the catalyst in a separate step by burning with air without cooling.

4. A process for the catalytic cracking of hydrocarbon oils boiling above about 311 F. which comprises preheating the oil to be cracked to an incipient cracking temperature between about 700 F. and 825 F., combining the preheated oil with a mixture of air and a hot regenerated catalyst consisting of a nely divided adsorptive cracking catalyst diluted with such an amount of a nely divided substantially non-adsorptive and non-combustible mineral diluent as to ailord a depth of cracking between 60% and 70%, said catalyst being at a temperature at least 90 F. above the cracking temperature and the amount of said air-catalyst mixture `being adjusted to heat the preheated oil to a cracking temperature above about 1022 F., retaining said oil in contact with said catalyst at said cracking temperature for a period of time corresponding to a weight hourly space velocity of .at least 6, separating cracked products rich in normally gaseous oleins from the catalyst and regenerating the catalyst in a separate step by burning with air without cooling.

5. A process for the catalytic cracking of hydrocarbon oils boiling above about 311 F, which comprises preheating the oil to be cracked to an incipient cracking temperature between about 700 F. and 825 F., combining the preheated oil with a mixture of air and a hot regenerated catalyst consisting of a finely divided adsorptive cracking catalyst diluted with such an amount of a finely divided substantially non-adsorptive and non-combustible mineral diluent as to afford a depth of cracking between 60% and '70%, said catalyst being at a temperature at least 90 F. above the cracking temperature and the amount of said air-catalyst mixture being adjusted to heat the preheated oil to a cracking temperature above about 1022 F., retaining said oil in Contact with said catalyst at said crackingtemperature for a period of time corresponding to a weight hourly space velocity of at least 6, separating cracked products rich in normally gaseousl olefns from the catalyst and regenerating the catalyst in a separate step by burning with air at a temperature between 1200 F. and 1400 F.

BERNARD S. GREENSFELDER.

STANLEY Z. PERRY.

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